A. Technical Field of Field of the Invention
This invention relates to the field of measuring acoustic waves within a fluid flow, and more particularly, to an acoustic sensor for measuring acoustic waves within a fluid flow while at the same time having means to eliminate unwanted noise that would otherwise interfere with the desired measurement and which noise is typically created by the acoustic sensor being inserted into the fluid flow.
B. Description of the Prior Art
In the field of measuring acoustic waves within fluid flows, it is important that the insertion of a probe or sensor into the fluid flow does not unnecessarily disturb the freestream value of the static pressure of the fluid. Freestream static pressure, which is steady in time, is the flow value of the fluid pressure in its undisturbed state. Acoustic waves posses acoustic pressures which are not steady in time but rather are time variable static pressures that increase and decrease about the freestream static pressure. Further, it is important that the measurement of the acoustic waves not be hindered by any noise that may be created by the insertion of the sensor into the fluid flow. It is desireable for the freestream static pressure to remain constant because any variation will be interpreted by the acoustic sensor as noise.
U.S. Pat. No. 3,914,997 ('997) of Pinckney issued Oct. 28, 1975, herein incorporated by reference, discloses a static pressure probe used in supersonic airflow to measure the static and the total pressure at the point of probe insertion. The '997 patent discloses a probe that is smaller in size relative to prior art devices. The probe of the '997 patent has three separate sections which allow the flow to occur at approximately the freestream static pressure at designated pressure ports along the length of the probe which are located approximately three (3) probe diameters as measured downstream from the tip of the probe itself. The probe of the '997 patent measures freestream static pressure (steady in time) and total pressure (steady in time) but not acoustic pressure (waves) (time varying). The probe of the '997 patent is specifically designed for use in supersonic flow and may have drawbacks when used in wind tunnels for measuring subsonic velocities. A major contributor to these drawbacks is that each of the three separate sections has relatively sharp corners which more than likely create noise that hinders the accurate measurements of acoustic waves within fluids flowing at subsonic velocities.
Accordingly, an object of the present invention is to provide a new and improved acoustic sensor for use in measuring acoustic waves within a fluid flowing at subsonic velocities.
Another object of the present invention is to provide a sensor that may be inserted into the fluid flow without unnecessrily disturbing the freestream value of the fluid static pressure.
It is a further object of the present invention to provide an acoustic sensor used for accurately measuring acoustic waves within a fluid flow in the subsonic, supersonic, or transonic velocities.